1. Field of the Invention
The present invention relates to a direct fuel injection-type spark-ignition internal combustion engine.
2. Description of the Related Art
There has heretofore been known a stratified charge combustion produced by directly injecting fuel into a cylinder to form a mixture (hereinafter referred to as a combustible mixture) that can be favorably ignited only in the vicinity of a spark plug, at the ignition timing, to burn a lean mixture in the cylinder as a whole. To carry out the stratified charge combustion, in general, the fuel injection valve injects fuel in the latter half of the compression stroke. It is intended that the thus injected fuel proceeds into a concave combustion chamber formed in the top surface of the piston, is vaporized by robbing heat from the high-temperature air and the wall surfaces of the combustion chamber, is deflected by the shape of the combustion chamber toward the spark plug, and forms a combustible mixture near the spark plug.
In general, the fuel injection valve injects fuel in a shape that is conically concentrated. Therefore, a relatively long period is required while the fuel injected in the last stage of fuel injection becomes a combustible mixture utilizing the heat from the wall surfaces of the combustion chamber. To ensure this period, therefore, the fuel injection end timing must be advanced. An amount of fuel which can be injected in the latter half of the compression stroke, therefore, inevitably decreases, and stratified charge combustion must be abandoned in high engine load operations in which a relatively large amount of fuel is required. It has therefore been desired to carry out the stratified charge combustion, which is effective in decreasing the consumption of fuel, over a wider range of engine operations.
Japanese Unexamined Patent Publication (Kokai) No. 9-158736 proposes injecting the fuel in the shape of a flat fan having a relatively small thickness by using a fuel injection valve having an injection hole in the shape of a slit. The thus injected fuel can rob heat from a wide area of the wall surfaces of the combustion chamber, making it possible to form a combustible mixture within a short period and to retard the timing for ending the injection of fuel. Thus, it is expected to increase an amount of injected fuel in the latter half of the compression stroke and to expand the range of the stratified charge combustion toward the high engine load side.
In the above prior art, fuel injected in a fan shape proceeds radially spreading along the bottom wall of the combustion chamber within a contained angle of the fan. At this time, all the parts of fuel in the direction of width thereof have velocity vectors along the bottom wall of the combustion chamber and maintain a radial relationship relative to each other. Thereafter, all the parts of fuel arrive at the side wall of the combustion chamber opposite to the fuel injection valve, and proceed along the opposing side wall. In general, the opposing side wall of the combustion chamber has an arcuate shape in a plan view and establishes such a positional relationship that the center of the contained angle of the fan of fuel is separated more than the center of the arcuate shape from the opposing side wall of the combustion chamber. When the fuel proceeds along the opposing side wall, therefore, the velocity vector of each part of fuel in the direction of width thereof is converted into a synthesized velocity vector of the upward velocity vector and the horizontal velocity vector directed to the center of the opposing side wall. It is thus intended to direct all parts of fuel toward the spark plug.
When the arcuate shape selected on the opposing side wall of the combustion chamber has a relatively small radius, the angle of collision of each part of fuel on the opposing side wall generally becomes small in a plan view. Therefore, the horizontal velocity vector generally increases in all parts of fuel. Particularly, fuel parts proceeding along the central portion of the opposing side wall would have already passed the vicinity of the spark plug at the ignition timing since the horizontal distance to the spark plug is relatively short.
When the radius of the arcuate shape is selected to be relatively large, on the other hand, the horizontal velocity vectors of all parts of fuel generally become small. Particularly, fuel parts proceeding along both sides of the opposing side wall have not yet been arrived in the vicinity of the spark plug at the ignition timing since the horizontal distance to the spark plug is relatively long. Thus, even when the opposing side wall of the combustion chamber is simply formed in an arcuate shape in a plan view, all parts of the fan-shaped fuel spray can not be concentrated near the spark plug at the ignition timing as intended. In the stratified charge combustion, therefore, the mixture formed near the spark plug becomes lean and a misfire can occur.
It is therefore an object of the present invention to reliably prevent a misfire in the stratified charge combustion in a direct fuel injection-type spark-ignition internal combustion engine in which fuel is injected in a nearly flat fan shape having a relatively small thickness.
According to the present invention, there is provided a direct fuel injection-type spark-ignition internal combustion engine comprising a spark plug, a cavity formed on the top surface of the piston, and a fuel injection valve for injecting fuel into the cavity in nearly a flat fan shape having a relatively small thickness, wherein an opposing side wall of the cavity opposed to the fuel injection valve, for leading the fuel to the vicinity of the spark plug, has an arcuate portion having a plurality of arcuate shapes in a plan view, the radius of the arcuate shape at both side parts of the arcuate portion in a plan view is smaller than the radius of arcuate shape at the center part of the arcuate portion in a plan view, and the opposing side wall has a deflecting portion to deflect the fuel toward the inside of the cavity.
The present invention will be more fully understood from the description of preferred embodiments of the invention set forth below, together with the accompanying drawings.